Conventionally, a scanning endoscope system configured to cause light guided by an optical fiber to scan in a spiral form with respect to an observation portion, and to image the observation portion by receiving reflected light from the observation portion is known (e.g., Domestic Republication No. JP 2008-514342A1 of PCT international application (hereafter, referred to as “patent document 1”)). The scanning endoscope system of this type includes a single mode optical fiber in an endoscope, and a proximal end of the optical fiber is held by a biaxial actuator in a state of a cantilever. The biaxial actuator vibrates (resonate) a tip of the optical fiber in two-dimension in accordance with a characteristic frequency while modulating and amplifying the amplitude of the vibration so that the tip of the optical fiber is driven in a spiral form. As a result, the illumination light guided by the optical fiber from the light source scans on the observation portion in a spiral form, and an image corresponding to an illumination range (a scanning area) is obtained based on returning light from the observation portion.
Recently, it has been proposed that the scanning endoscope system as shown in patent document 1 can be applied to a scanning confocal endoscope system (e.g., Japanese Patent Provisional Publication No. 2011-255015A (hereafter, referred to as “patent document 2”)). The scanning confocal endoscope system is configured to emit laser light to a living tissue and to extract only a component, obtained through a pin hole arranged at a position conjugate with a focal point of a confocal optical system, of fluorescence emitted from the living tissue so that observation can be achieved at a magnification higher than that of an observation image obtained by a normal endoscope optical system. The scanning confocal endoscope system described in patent document 2 is configured to be able to observe a minute subject which cannot be observed at a magnification of an observation image obtained by the normal endoscope optical system and to be able to observe a cross section of a living tissue, by scanning in two dimension or three dimension with laser light for a particular narrow area of a living tissue.
In the system described in patent document 1 or 2, reflected light or fluorescence from the scanning area (the observation portion) is received at timings of a predetermined cycle (hereafter referred to as “sampling points”), and intensity information at each sampling point is assigned to a display coordinate of a monitor (a pixel position of an endoscopic image) to display a two-dimensional endoscopic image. Therefore, in order to generate an endoscopic image having a high degree of reproducibility without distortion, it is necessary to set a scanning position of each sampling point to precisely match the display coordinate of the monitor. For this reason, in the scanning endoscope system of this type, calibration is performed while monitoring an actual scanning pattern (scanning trajectory) so as to achieve an ideal scanning pattern (patent document 1).